The present invention relates to video effects, and more particularly to a single channel video push effect to provide a high quality push effect while using only a single video effects module.
One way to make a transition from one video source to another is by doing a "push" in which the new video slides onto a viewing screen and appears to "push" the old video off the viewing screen at the same time, as is shown in FIG. 1 where the dotted lines represent the original source images and the heavy lines represent the viewed image. The transition appears as if the images represented by the two video sources were connected side-by-side and a camera is panned from one image to the other.
The push effect is a transition that appears over several video frames, with each successive frame yielding an image with the new video source slid further onto the screen and the old video source shifted correspondingly off the screen. A single frame having the old and the new video sources on the screen may be considered to be a "push snapshot." The moving push transition is a series of these snapshots with each successive snapshot showing more of the new video source and less of the old. The push transition therefore requires a means for generating these snapshots and a means for sequencing through the snapshots.
Currently there are two ways to perform push transitions. The first way is to use two time base correctors (TBCs) to individually shift each video source image, one in one direction and the other in the opposite direction. The two images are then combined to complete the push snapshot. For example, as shown in FIG. 2, the images appear to be overlaid and the old image is translated in one direction by a distance X, where X ranges from zero to one, one representing a full screen distance. The new image is translated in the opposite direction by a distance (1-X). The two images are then combined using a key signal that determines which part of the combined image comes from the old video source and which from the new video source. In other words the control key specifies that the first X portion of the screen, vacated by the old image, is filled with the new image, and the next 1-X portion of the screen, vacated by the new image, is filled with the old image. The result is that the new image appears to have pushed the old image a distance X across the screen. The second method of creating the push snapshot is similar to the first method, except the translations are done with two video effect modules.
These methods have some drawbacks. Specifically for the first method commercial TBCs have timing accuracy problems and sometimes poor video quality, while for the second method two expensive video effects channels are tied up to create a single video effect.
Therefore what is desired is a single channel video push effect that produces high quality video while using only a single video effects module.